1. Field of the Invention
The present invention relates to a sensor incorporated wheel support bearing assembly having a load sensor built therein for detecting a load imposed on the bearing assembly for the support of a vehicle wheel.
2. Description of the Prior Art
For safety travel of an automotive vehicle, the wheel support bearing assembly has hitherto been well known in the art, which is equipped with a sensor for detecting the rotational speed of one of automotive wheels. While the automobile traveling safety precaution is generally taken by detecting the rotational speed of a vehicle wheel of various parts, but it is not sufficient with only the rotational speed of the wheel and, therefore, it is desired to achieve a control for safety purpose with the use of other sensor signals.
In view of the above, it may be contemplated to achieve the vehicle attitude control based on a load acting on each of the wheels during travel of an automotive vehicle. By way of example, a large load acts on the outside wheels during the cornering, on the wheels on one side during the run along left and right inclined road surfaces or on the front wheels during the braking, and, thus, a varying load acts on the vehicle wheels. Also, even in the case of the uneven live load, the loads acting on those wheels tend to become uneven. For this reason, if the loads acting on the wheels can be detected as needed, suspension systems for the vehicle wheels can be controlled beforehand based on results of detection of the loads so that the attitude control of the automotive vehicle during the traveling thereof (for example, prevention of a rolling motion during the cornering, prevention of diving of the front wheels during the braking, and prevention of diving of the vehicle wheels brought about by an uneven distribution of live loads) can be accomplished. However, no appropriate space for installation of the load sensor for detecting the load acting on the respective vehicle wheel is available and, therefore, the attitude control through the detection of the load can hardly be realized.
Also, in the event in the near future the steer-by-wire is introduced and the system, in which the wheel axle and the steering are not coupled mechanically with each other, is increasingly used, information on the road surface comes to be required to transmit to the steering wheel hold by a driver by detecting a wheel axis direction load.
In order to meet those needs hitherto recognized, a wheel support bearing assembly having a strain gauge attached to an outer ring member thereof for detecting a strain has been suggested. (See, for example, the Japanese Laid-open Patent Publication No. 2003-530565, published Oct. 14, 2003.)
An outer ring member of the wheel support bearing assembly is a bearing component part having a raceway surface defined therein and required to have a strength, and is manufactured through complicated process steps including, for example, a plastic forming, a turning process, a heat treatment and a grinding process. Accordingly, while strain gauge is attached to the outer ring such as disclosed in the patent document discussed above, there is a problem in that the productivity is low and the cost of manufacture thereof during a mass production tends to become high. Also, it is not easy to detect with high sensitivity, a strain occurring in the outer ring and, when a result of such detection is utilized in controlling the vehicle attitude of an automotive vehicle then travelling, a problem will arise in association with the accuracy of the control.